1. Field of the Invention
The present invention relates to a manual rotation type display device for aerially displaying an image utilizing a residual image effect by rotating the display device about a finger of a user's hand.
2. Description of the Related Art
Japanese Unexamined Utility Model Publication (Kokai) No. Heisei 3-50541 discloses a rotary scan type aerial display device. In the disclosed construction, the display device is mounted on a rotary body, such as a wheel of a bicycle. With respect to the center of rotation, a plurality of light emitting elements are arranged in alignment in the radial direction for forming a light emitting cell array. When the display device is rotated together with the wheel, the light emitting cell array is scanned within a rotating trace of the wheel. With a combination of the rotary scanning by the light emitting cell array and time division illumination control for respective light emitting elements, an aerial image can be formed by the residual image effect on the rotatingly scanned surface.
In the shown construction, a position signal outputting means such as a magnet is mounted on a supporting plane such as a frame of the bicycle. On the other hand, the device body is provided with a signal generating means for generating a synchronization signal every time the device body moves across the closest position to the position signal outputting means. Namely, the synchronization signal is generated once during one cycle of rotation of the rotary body. Image display operation is initiated at a timing delayed from the occurrence of the synchronization signal for a predetermined delay period At. Also, a most recent average period of the synchronization signal which is inversely proportional to the rotation speed is constantly obtained. As a result, the image can be displayed at a predetermined rotational phase position even when the rotation speed fluctuates.
That is, in synchronism with rotational scan of the light emitting cell array, the image data of the image to be displayed is sequentially read out from a memory. Then, respective light emitting cells in the light emitting cell array are selectively illuminated according to the read out image data. Here, it is important to establish synchronization between rotation of the device and the display control so as to stably display the image.
In case of the display device in which the light emitting cell array is driven at a constant rotational speed by means of a motor or so forth, such as that illustrated in Japanese Unexamined Patent Publication No. 2-213892, the foregoing feedback type synchronization control may not be necessary. However, for the display device adapted to the rotary body which may irregularly fluctuate the rotation speed, it is inherent to provide certain synchronization control for stability of the displayed image.
On the other hand, a manually operated scan type aerial display device has been proposed in commonly owned European Patent First Publication No. 05 46 844, published on Jun. 16, 1993 (corresponding U.S. patent application which has now been pending under U.S. patent application Ser. No. 07/991,547, filed on Dec. 11, 1992). The disclosed swing or scan type aerial display system is adapted to aerially display a desired visual image utilizing a residual image effect of a moving light emitting cell array. In order to establish synchronization of the motion of said moving light emitting cell array and illuminating timing of individual cells in the light emitting cell array, the motion behavior of the system is monitored and timing to drive each individual cell is controlled in relation to the monitored motion behavior of the light emitting cell array, so that the desired image becomes visible at a desired position and desired configuration. The aerial display system includes a display control circuit having a memory for storing an image data corresponding to the image to be displayed. The display control circuit receives the output of a sensor monitoring the swing motion of the light emitting cell array for selectively illuminating the individual cells in synchronism with the swing motion to aerially display the desired image. More specifically, the display control circuit reads out an image data in a bit map format in a predetermined order per line to line at an appropriate speed for driving the individual cells to illuminate and obscure depending on the lighting pattern at respective lines in synchronism with the swing motion of the main body. Then, by the afterimage or residual image effect, aerial image can be displayed in the aerial space.
The above-identified commonly owned prior invention provides significant gain in manually operated scan type display as far as the display device is operated in reciprocal manner. In case of the rotary type display device, however, the prior proposed invention is not applicable as it is since such type of display device has no stroke end and a direction of acceleration does not vary periodically. This means that, in case of the rotary type display device, the synchronization mechanism which is successfully applied in the prior invention, is not fully effective.